Reflow soldering is widely performed in which a paste-like solder is applied or printed in advance to a necessary location on a circuit board and thereafter the solder is heated. In this reflow soldering, electronic devices or the like are positioned at the locations of the circuit board having the solder paste applied or printed thereto and are heated in a reflow oven. Thereby, these electronic devices or the like are soldered to the circuit board.
In this regard, a thought is given to reflow soldering in which a through-hole of a circuit board is filled with a solder paste in advance and a rod-like terminal is inserted thereinto. In this case, a part of the solder paste within the through-hole is pushed out by inserting the terminal into the through-hole. Therefore, without a countermeasure taken in advance, the solder paste having been pushed out and adhering to the tip of the terminal tends to melt and drip when being heated in the reflow oven. When the solder drips, an insufficiency of solder for soldering occurs, which may result in a soldering defect.
JP2011-54528A suggests forming a tip portion of the terminal into a shape dissimilar from an inner-peripheral shape of the through-hole by a pressing process. In addition, this PLT1 further suggests forming in the tip portion of the terminal a recessed groove extending in a direction of insertion into the through-hole. JP2011-54528A makes a statement to the effect that the recessed groove actively brings a capillary action about to improve solder wicking along the recessed groove.
The recessed groove disclosed in JP2011-54528A is a groove having a constant cross-section in the longitudinal direction or having a cross-section enlarging as the distance from the tip increases. Therefore, the capillary action is not sufficiently brought about and not all the solder melted can be prevented from dripping, so that the possibility still remains that the insufficiency of solder for soldering may occur.